Āb anbār is an underground structure, constructed in the past to store freshwater for domestic uses. The water reservoir was fed from a near shallow qanat. All of the water reservoirs had a storage tank whose dimensions could be different depending on the amount of qanat discharge and the demand for water. Most of the storage tanks were made of sārooj.
Sārooj is a combination of lime, clay, and chipped straws, for cementing the bricks or stones together.
The different parts of a water reservoir were: storage tank, the roof of the storage tank, wind tower, stairway and ornamental portal. A water reservoir does not have to have all of above mentioned parts.
Water reservoirs were filled in the wet seasons with the water of a shallow qanat nearby and in the dry seasons could provide people with the cool and fresh water.
Soon public ab anbars were constructed throughout cities across Persia such as Qazvin, Yazd, Naeen, Kashan, Zavareh, Ray, Shiraz, Herat, Balkh, and others. At the beginning of the 20th century, the number of public ab anbars in Qazvin, for example, was recorded to be 151. Yet Iran still has 30,000 active Qanat systems today.
Accounts differ, but the water quality generally seemed to be satisfactory. Water temperatures of Kashan’s famous Qanat of Chashmeh-i Soleiman amidst the July heat is typically around 25 degrees Celsius. Furthermore, ab anbars tend to further lower the temperature of the water due to the fascinating heat resistance properties of the construction material used.
Near freezing temperatures of the water can readily be observed in the desert central city of Naeen during summer, inside an ab anbar that employs multiple windcatchers. Thus the Qanat/ab anbar system was easily able to supply the needs of many growing cities (such as medieval Qazvin) year round.